To remove the paint, dirt or other surface coating from a substrate such as a surface to be painted or cleaned, a blasting system is desirable and effective. There are a variety of blasting processes for these purposes, including, but not limited to, water blasting, dry abrasive blasting, and wet abrasive blasting. In certain applications, abrasive blasting systems are able to efficiently clean or remove a coating without damaging the underlying metal or other substrate, although in other applications, a certain degree of surface roughening may be desired.
The use of dry abrasive blasting with particles, such as those used in conventional sand blasting, may result in excessive surface roughness and other damage to the substrate. Typical blast particles are hard and abrasive in order to increase the efficiency of the blasting operation but may, therefore, result in damage to the substrate. Soft recyclable blast particles are sometimes substituted to avoid surface damage. These recyclable blast particles include, but are not limited to, agricultural products such as crushed walnut shells, crushed pistachio shells, corn husks, and rice hulls. Plastic particles are sometimes used to reduce substrate surface damage but may also result in a reduction in efficiency of the blasting operation.
Wet abrasive systems have been used to also control and reduce surface damage. Wet abrasive systems combine the benefits of water blasting systems with dry abrasive blasting systems. In wet abrasive blasting, the fluid can encapsulate particles of the abrasive media to simultaneously add mass to the abrasive and buffer the impact of the abrasive against the substrate to reduce potential surface damage, but still effectively strip or clean the surface while also reducing the dust produced by dry blasting. However, wet abrasive systems require efficient mixing of the slurry with a gas stream to produce a consistent blast stream comprising a three-phase mixture of fluid, solid abrasive, and gas. If the mixing of slurry and pressurized gas is not well controlled, the blasting process is less efficient and, therefore, the benefits of the wet abrasive system are not fully realized.
There is a need for a wet abrasive system that is easier to control in order for the benefits of a wet abrasive system to be more fully realized. In the past, the control has been overly complicated and required extensive training before an operator became fully proficient. Even then, there remained the possibility of operator error because multiple selector valves have at least nine different positions which could be selected (only one being the correct position); therefore, there were eight possible erroneous positions for any one function.